I think the most important factor is not really screen resolution or size, but "cursor precision". I'm fine with HN on mobile, but it is really hard to press t

I think the most important factor is not really screen resolution or size, but "cursor precision". I'm fine with HN on mobile, but it is really hard to press the buttons with my large fingers on a mobile screen. But much easier on a 800x600 monitor using a ball mouse. For HN I don't really mind, as a pinch to zoom. To check for touch, there is `Navigator.maxTouchPoints` but this might backfire on some laptop which have touch screen (which you usually use for drawing rather than UI, but your mileage may vary). But I think the core issue is much earlier in design. Many websites and app have complicated design/UI while it could be simpler, and they split their UI into mobile and desktop very early in the design process, which leads to two very different version. And while I agree that mobile and desktop are different experience, I think you can keep them close in term of UI and UX. For example, let's say you want tooltip, on desktop this is a normal UI control which is natural, but on mobile it is not, so instead of using tooltip on desktop and "think of something" when doing the mobile version, we need to design early for both. Today, many website and apps are designed with a "mobile first" mindset, and this cause problem when used on desktop. The solution is not better detection of either platform, but better design to keep them as close as possible. Of course, there is also the issue of scaling text vs scaling the whole site, and this is not very well handled by many website, even with the "let's use em/rem units".